Method of operating a refrigeration system using a chlorine containing halo-alkane as a refrigerant



United States Patent METHOD OF OPERATING A REFRIGERATION SYSTEM USlNG ACHLORINE CONTAINING 'HALO-ALKANE AS A REFRIGERANT James R. Davidson,Iselin, and William Elena, Union,

N. J assignors to Esso Research and Engineering Company, a corporationof Delaware NoDrawing. ApplicationDecember 1, 1953 Serial No. 395,600

6 Claims. (Cl. 252-325) The present invention relates to improved oilcompositions for use in compression-type mechanical refrigerationsystems. It particularly relates to such compositions having improvedstability and compatability with halo-alkane refrigerants used inenclosed compressor-type refrigeration systems to lubricate the movingparts thereof.

It has now been found and is the subject of this invention thatlubricating oils used in. conjunction with halo-alkane refrigerants inrefrigeration systems are improved in stability and life by the additionof relatively small amounts of oil-soluble alkali metal salts of phosphoric acid esters.

Self-contained compressor refrigeration systems such as mechanicalrefrigerators, air conditioning units, etc. include acompression-expansion system in which a gaseous refrigerant iscompressed and reduced to a liquid by cooling at a relatively hightemperature level. The liquid is then passed through an expansion valvewhere its pressure is reduced and the liquid evaporates to absorb itslatent heat and the heat from the medium to be cooled. Alternate cyclesof compression and expansion are carried out. The system is enclosed andmust therefore contain a lubricating oil to lubricate moving parts ofthe system, such as the compressor, that are subject to frictionalcontact. The oil and refrigerant form a mutually soluble composition inthe high temperature Zone, the refrigerant being the predominantcomponent.

The lubricating oil to be used in such systems should have a number ofspecial characteristics that enable it to lubricate effectively for aperiod of many years without being replaced. It should have a low pourpoint so that it will flow freely at extremely low temperatures. It musthave a low fioc point, i. e., a low temperature at which flocculentprecipitation occurs in a mixture of the lubricant and refrigerant. Itshould also be stable against sludge formation or the formation of otherundesirable bodies that will lead to clogging of orifices and depositionof solids in the system.

Refined mineral oil base stocks, certain synthetic oils such as olefinpolymers, etc., are useful lubricants for such systems because of theirexcellent oiliness characteristics, low pour points, and low fiocpoints, particularly when suitable additives are employed. However, suchbase stocks tend to deteriorate in the presence of conventionalhalo-alkane refrigerants, particularly those containing chlorine. Itappears that the oil and refrigerant undergo a reaction, aided by thecatalytic action of iron or other metals in the system, to form hydrogenchloride. The acid in turn evidently degrades the oil to form sludge. Ithas been noted for example that the compressor discharge valve, which isthe highest temperature point in the compression system, becomes coatedWith a hard carbonaceous material which can eventually cause breakage ofthe valve. The used Oil also eventually becomes discolored.

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The reasons for these difiiculties are: not entirely understood.However, the mechanisms are quite different from those encountered inconventional lubrication wherein the lubricating oil is in contact withairfmoisture and metal which results in oxidation of the oil andcorrosion of metal parts. This difference is emphasized by the fact thatconventional motor oil 'antioxidant and related additives, such as forexample metal naphthenates, phenols, amines, various metal deactivators,etc., do not prevent degradation of refrigeration oils. Indeed,conventional additives frequently aggravate this difficulty inrefrigeration systems. As an example, aromatic amines, which are knownlubricant antioxidant additives, 'are quite effective for reducing liocpoints of refrigerating oils when used in small con centrations.However, these same additives promote color degradation and sludgeformation in refrigerating oils when used in the relatively largeamounts taught to be effective for retarding oxidation effects inconventional motor oils and the like. It is seen that an additivedesigned to improve the stability of refrigerator oils must have specialqualifications to meet unique problems. Furthermore, refrigeration oiladditives should be soluble in the oil base stock over a wide range oftemperature conditions and should not impair the floc point of the oil.

in accordance with the present invention, it has been found that alkalimetal salts of phosphoric acid hydrocarbon esters are effectiveadditives for refrigerating oils used in conjunction with halo-alkanerefrigerants. Such compositions have greatly enhanced stability againstdeterioration and sludge formation, low pour points and other desirablecharacteristics required of such oils. These additives containingsuitable oil-solubilizinghydrocarbon substituent groups are soluble overa wide range of temperatures.

Although various metal ester phosphates have been used heretofore asdetergent additives, corrosion inhibitors, etc., for conventional motoroils and the like, they have been found to be inducers of thermaldecomposition and carbon formation for such uses. It is thereforesurprising that m the alkali metal salts reduce discoloration and sludgeformation in refrigeration'systems. It is not desired to be bound bytheoretical considera tions, but it is believed in the instant case thatthese salts may act as buffers in ameliorating the harmful effects ofacidic bodies that are formed and cause further degradation of the oiland/or refrigerant. Regardless of the mechanism involved, the presenceof haloalkanes in such systems introduces lubrication problems notencountered in other conventional systems not containing suchhalo-alkanes in large concentrations, and the addition agents of thepresent invention minimize such difficulties.

The present invention will be clearly illustrated by reference to thefollowing examples:

Example I .---Preparation of alkali metal octadecenyl phosphates Thisproduct was prepared by heating together 80.4 g. (0.3 mol) of Ocenol(commercial oleyl alcoholC H OI-I) and 14.2 g. (0.1 mol) of P 0 forabout one hour at C. The reaction mixture was cooled, and then 12 g.(0.3 mol) of NaOH and 100 g. of water were added with stirring. 100 ml.of ethyl alcohol were added to the resulting mixture, to precipitate aninsoluble material. The precipitate was removed by filtration. Thefiltrate was diluted with water and extracted with ether. The etherextract was dried over sodium sulfate, and the ether was removed on asteam bath.

The residue was finally dried in a vacuum oven at 100 C,

The dry product consisted of an amber-colored viscous, soft resin,having an acid neutralization number of about 23 mg. KOH per gram. Itwas substantially a mixture of equal portions of mono-sodiumdi(octadecenyl) phosphate and di-sodium octadecenyl phosphate. A smallamount of acid derivatives was also present.

Example II.Testing refrigeration compositions Anacid-treated Coastal oildistillate having an S. U. S. viscosity at 210 F. of about 55 had addedto it 2% by weight of the product of Example I. A small amount ofundissolved material was settled out of the blend. This blend and aportion of the oil base stock per se were submitted to various tests andinspections, the

1 In presence of iron wire as catalyst.

The oil blend containing the sodium alkenyl phosphates had excellentpour characteristics and was much more stable than the uninhibited oil.

Each of the above oils was subjected to a sealed-tube stability testcarried out as follows: A mixture of 1 part Freon-l2(dichlorodifluoromethane) and 2 parts oil was introduced into a heavyglass tube containing iron wire catalyst, and the tube was sealed. Thesealed tube was then stored at a temperature of about 350 F. The tubewas periodically inspected in front of a standard light to determine theextent of discoloration and sludge formation. The oil life is designatedas the number of days under these storage conditions that the oil willtransmit light. This accelerated test has been found to correlate wellwith full-scale operations in compression refrigeration systems.

It was found that the mixture of Freon-l2 and oil base stock per sediscolored rapidly, formed sludge in the tube and on the wire and wouldnot transmit light after 27 days storage. The mixture containing theinhibitor of the present invention was still clear and transmitted lightafter 95 days storage at which time the test was discontinued. There wasno evidence of sludge formation and no visible color degradation of theoil after this time.

The preferred alkali metal salts of phosphoric acid esters added to theoils of the present invention may be illustrated by the formula whereinthe X groups are selected from the class con sisting of hydrogen, alkalimetals, such as sodium, potas sium and lithium, preferably sodium, andhydrocarbon radicals, and wherein at least one X group is an alkalimetal and at least one X group is a hydrocarbon radical; preferably allof the X groups are metal and hydrocarbon.

Since the alkali metal phosphates are relatively dithcultly soluble inmost lubricating oils, the hydrocarbon groups are sufficiently high inmolecular weight to inrpart the desired degree of oil solubility to thecompound at the extremely low temperature prevailing in certain portionsof the refrigeration systems. Therefore, the

,4 metal phosphate esters desirably contain a total of at least carbonatoms, preferably above carbon atoms, in the hydrocarbon groups.

Suitable hydrocarbon groups include alkyl, alkenyl, cycloalkyl, alkaryl,aralkyl and related groups, the aliphatic members being preferred.Individual groups may have in the range of about 6 to 30, preferably 12to 24, carbon atoms. The phosphates are readily prepared by conventionalprocedures, such as by reacting an ester acid phosphate with an alkalimetal hydroxide, by reacting an alcohol or phenol with P 0 and sodiumhydroxide, etc.

Suitable specific metal salts that may be used include sodium dodecylphosphate, sodium decyl acid phosphate,

dipotassium oleyl phosphate, sodium di(buty1cyclohexyl) phosphate,disodium cetyl phosphate, sodium di(cetylphenyl) phosphate, sodiumnaphthenyl phosphate, potassium di(C -C wax) phosphate, disodiumolylcyclohexyl phosphate, their mixtures, and the like.

The amount of the phosphate added to the oil base stock to form therefrigerating oil will depend on such considerations as potency andsolubility of the additive, and the relative instability of therefrigerant and oil base stock. Amounts in the range of about 0.05 to5.0% by weight based on the oil, will generally suffice, with preferredamounts being about 0.1 to 2% by weight. The alkali metal salts aregenerally difficult to dissolve in mineral oils in amounts above about 1to 2% unless large hydrocarbon solubilizing groups are present. Thus atotal of about to carbon atoms may be needed in the phosphatehydrocarbon radicals if relatively large amounts of the additive are tobe used.

The oil base stocks useful for refrigerating oils are preferably derivedfrom various paraflinic, naphthenic and mixed-base crude mineral oils,but naphthenic-type distillates, such as Coastals, are preferred. Thebase stock may be refined by conventional procedures such as bydewaxing, solvent extraction, acid treating, clay contacting, etc. Othersuitable lubricating oils include synthetic oils such as polymerizedolefins, e. g., polyisobutylenes, and the like. Essentially hydrocarbonoils are preferred. Oils having S. U. S. viscosities at 210 F. in therange of about 30 to 160, preferably below 100, and pour points below-l5 F., especially below 25 F. are preferred.

1 Floc points of below 25 F. are also preferred.

In addition to the additives of the present invention, othercharacteristic improving additives may be added to the oil base. Theseinclude pour point depressors, such as wax-naphthalene condensationproducts, maleate ester copolymers, fumarate ester copolymers, etc.;floc point reducers such as phenol amine compounds, etc.

Suitable refrigerants used in the compression systems in conjunctionwith the above lubricating oils include the halogenated substitutedalkanes, particularly of the lower alkanes such as methane. Specifictypes include chloroalkanes, chloro-fiuoro-alkanes and the like.Specific refrigerants include dichlorodifiuoromethane, methyl chloride,methylene chloride monofluorotrichloromethane,dichloromonofluoromethane, etc. The present invention appliesparticularly to the chlorine-containing halo-alkanes because thesematerials are generally less stable than those containing only fluorine,such as fluoroform.

The refrigerant-oil composition of the present invention will contain amajor portion of the refrigerant and a minor proportion, usually belowabout 10 weight percent, of the inhibited oil. In actual operation, oncethe desired amount of refrigerant and inhibited oil have been sealedinto the unit, the solution of compressed liquid refrigerant and usuallyno more than 27% of oil, based on the refrigerant, will be carriedthrough the compressor discharge valve (the high temperature point) intothe condensing, expansion and evaporation zones. The evaporation zonewill usually contain an oil separator that returns the oil to thecompression zone by a different route to that followed by the vaporizedrefrigerant. Methods of operating such refrigeration systems are wellknown to the art and will not be described in detail herein.

What is claimed is:

1. In the method of operating a sealed mechanicalcompression-expansion-type refrigeration system using achlofine-containing halo-alkane as a refrigerant and an essentiallyhydrocarbon lubricating oil for lubricating the internal moving partsthereof subject to friction, and wherein said refrigerant and oil comeinto contact with one another resulting in the formation of sludge andother degradation products, the improvement in accordance with which theformation of sludge and other degradation products is reduced whichcomprises lubricating said refrigeration system with a lubricating oilcomposition comprising a mineral lubricating oil base stock having an S.U. S. viscosity at 210 F. in the range of about 30 to 160 and a pourpoint below about 25 F. containing dissolved therein in the range ofabout 0.05 to 5% by weight of an alkali metal salt of a phosphoric acidester containing at least 10 carbon atoms.

2. A method as in claim 1 wherein said alkali metal is sodium.

3. A method as in claim 2 wherein said salt is a sodium aliphatic esterphosphate.

4. A method as in claim 3 wherein the aliphatic groups in said phosphateare alkenyl radicals having in the range of l2-24 carbon atoms.

5. A method as in claim 4 wherein said refrigerant isdichlorodifiuoromethane.

6. A method as in claim 5 wherein said lubricating oil in said system isused in an amount below about 10 weight based on the amount ofrefrigerant therein.

The Refrigerating Data Book, 5th ed. 1953, Amer. Society of Refrig.Eng., pages 189-196.

1. IN THE METHOD OF OPERATING A SEALED MECHNICALCOMPRESSION-EXPANSION-TYPE REFRIGERATION SYSTEM USING ACHLORINE-CONTAINING HALO-ALKALANE AS A REFRIGERANT AND AN ESSENTIALLYHYDROCARBON LUBRICATING OIL FOR LUBRICATING THE INTERNAL MOVING PARTSTHEREOF SUBJECT TO FRICTION, AND WHEREIN SAID REFRIGERANT AND OIL COPNEINTO CONACT WITH ONE ANOTHER RESULTING IN TEH FORMATION OF SLUDGE ANDOTHER DEGRADATION PRODUCTS, THE IMPROVEMEMTS IN ACCORDANCE WITH WHICHTHE FORMATION OF SLUDGE AND OTHER DEGGRADTION PRODUCTS IS REDUCED WHICHCOMPRISES LUBRICATING SID REFRIGERATION SYSTEM WITH A LUBRICATINB OILCOMPOSITION COMPRISING AMINERAL LUBRICATING OIL BSASE COMPOSITION COMS.U. S. VISCOSITY AT 210* F. IN THE RANGE OF ABOUT 30 TO 160 AND A POURPOINT BELOW ABOUT-25 F. CONTAINING DISSOLVED THEREIN IN THE RANGE OFABOUT 0.05 TO 5% BY WEIGHT OF AN ALKALI METAL SALT OF A PHOSPHORIC ACIDESTER CONTAINING AT LEAST 10 CARBOM ATOMS.